...Since 2004, the most impressive visible domestic victories against terrorism have involved elaborate sting operations. (Faisal Shahzad, who set a car bomb in New York’s Times Square, would have succeeded if two street vendors hadn’t noticed smoke coming from the car.) Since Congress closed domestic courts to prosecutions of terrorists held in Guantanamo Bay, Cuba, all the high-profile terror convictions in U.S. courts have come from setup operations except for Shahzad.

Of course, it is conceivable that other, genuine domestic terror operations have been thwarted without arrests being made -- but outside the realm of “Homeland” or “24,” such a scenario is highly unlikely. The value of a public conviction is too high for law enforcement to pass up. More to the point, the risk of letting a would-be terrorist walk around freely is too great for law enforcement to take.

The upshot is that our domestic anti-terror system has been reduced to a series of sting operations. Those who have gotten through the cracks, such as Army Major Nidal Hasan, who is accused of killing 13 at Fort Hood in 2009, acted alone and remained undetected. Unless you believe that the people caught in stings were going to commit acts of terror on their own, it’s hard to escape the conclusion that there isn’t much connection between domestic counterterror operations and the actual terror threats that surely still exist.

Would those convicted for attempting terror in concert with undercover agents have acted alone? Entrapment law says a jury must believe that the accused had a prior inclination to commit the crime. But even if we accept that a jury would actually throw out a terror charge on entrapment grounds, proving prior inclination is a far cry from proving that the accused would have acted without the assistance and encouragement of law enforcement.

In several well-publicized cases, it seems almost certain that no terrorist attack would have occurred without the government’s active support. The Fort Dix Six were a group of New Jersey men who shot semi-automatic weapons in the woods, played paintball and sat around Dunkin’ Donuts talking about jihad. They were convicted after an FBI undercover agent offered to sell them guns and RPGs for what was said to be an attack on Fort Dix, where one of them had delivered pizzas.

In a few more extreme cases, run not by the FBI but the New York Police Department, the would-be terrorists were either unbalanced or of low intelligence, and sometimes both. Indeed, given the ubiquity of such stings, you have to wonder about the intelligence and stability of anyone who allows himself to be guided into terror by a stranger whose identity he hasn’t reliably verified....